The determination of color or shade of an object is a process that is frequently performed in the field of dentistry. For example, to perform a dental restoration of a damaged tooth, a dentist may visually compare the color of the tooth to be replaced with an assortment of shade tabs. These shade tabs are physical tabs representing the color of commercially available restorative materials, such as ceramics. The tabs include the exact specification of materials needed to produce a restorative tooth with the shade of the original tooth as determined by the dentist's visual comparison. Once the dentist finds a shade tab that matches the color of the tooth, or remaining adjacent teeth in some cases, he/she is in a position to manufacture the required restoration. This process, however, is very time consuming, subjective, and frequently results in poorly shaded restorations.
To address these and other problems associated with visual color comparisons, instruments for measuring tooth color have been developed and are commercially available. Such instruments typically utilize a reflectance-based measurement arrangement wherein a light source illuminates the tooth and one or more light sensors detect a portion of the light reflected from the tooth surface. The light sensor output is then processed to determine spectral characteristics of the reflected light and, thus, the tooth color.
Conventional color measurement instruments for use in dental applications are not without their drawbacks, however. First, the optical design of such instruments typically requires the instrument to be precisely presented at a pre-determined angle with respect to the tooth surface in order to ensure accurate measurements. Because these instruments are usually configured for hand-held use, measurement accuracy is necessarily limited by the user's ability to precisely maintain the proper presentation angle. Second, in cases where the instruments are configured for insertion into a patient's mouth, it may be necessary to clean and sterilize at least a portion of the instrument between uses. For many conventional instrument configurations, this process is time-consuming and otherwise inconvenient.
To minimize cleaning/sterilization problems, some instrument designs incorporate a disposable “bag” for sealing that portion of the instrument inserted into the mouth. However, this arrangement invariably introduces measurement error due to the absorptive, scattering and reflective effects of the bag upon light transmitted to and reflected from the tooth surface. Other instrument designs utilize a disposable light guide for contacting the tooth and injecting light therein. This illumination arrangement, however, does not provide a standard measurement geometry representative of normal viewing conditions. As a result, color measurements may not correlate well with visual assessments. Third, the ability of conventional instruments to block ambient light present during normal room illumination is limited, further reducing measurement accuracy.
Thus, a need remains for apparatus, systems and methods for color measurement in the dental field that overcome the limitations and disadvantages of existing color measurement modalities.